English language is a hobby.
Rule 1. The language has rules. These might be obscure or not, but the language is inherently governed by rules. A linguist might study a foreign language based on deeper knowledge than a non-linguist. It is up to someone to embrace deeper rules of language.
Rule 2. People often assume (not entirely correctly) that being "native" is equivalent to being proficient or expert in a language.
Rule 3. Context is very important in analyzing a text fragment